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Topic: How do you dry a solvent...  (Read 16130 times)

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Offline dudeman

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How do you dry a solvent...
« on: December 13, 2009, 01:36:16 AM »
I wondering how to dry a solvent. I looked it up and found out a bit but I always seem to learn more from you guys so if you have a few ways to dry a solvent or even other things feel free to drop them on my head...

I know of one that I learned on you tube which is pretty cool... You seal a cup of sodium hydroxide and the cup holding what your trying to dry in a bag like an oil that has a little water in it...

Offline Markovnikov

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Re: How do you dry a solvent...
« Reply #1 on: December 13, 2009, 02:52:14 AM »
We drop small pieces of sodium and drop them in the solvent can and let them stay over night. If you still can see pieces of sodium the day after, then they're dry.

Offline dudeman

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Re: How do you dry a solvent...
« Reply #2 on: December 13, 2009, 04:36:37 AM »
That sounds wasteful sonny...

Offline nj_bartel

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Re: How do you dry a solvent...
« Reply #3 on: December 13, 2009, 05:34:49 AM »
It's just how it's done.  If you're moving a solvent to an inert atmosphere, you dry with sodium / sodium hydride.  Very, very, very dry.

Offline tmartin

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Re: How do you dry a solvent...
« Reply #4 on: December 13, 2009, 09:45:39 AM »
We also distill some solvents over sodium (THF), and in some cases I think CaH is used (for acetonitrile).  Also, for commonly used solvents, such as methylene chloride, ether, THF, and toluene, we have a solvent system set up that passes the solvents over an alumina column that dries them.  That system is not quite as easy to set up as a thermal still with Na, Ca, or CaH though.

Offline g-bones

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Re: How do you dry a solvent...
« Reply #5 on: December 13, 2009, 02:50:50 PM »
Solvent stills are usually tops. CHCl2 is usually dried over CaH2, and ethers over sodium (with benzophenone as an indicator).  if you are just looking to grab just a small personal amount of dry solvent you can set up your own smaller distillation apparatus.  make sure to have all of the glassware you will be using in the oven over night (you can also flame dry it, but the jacket on the condensor will prevent the condensor from being dried, so that needs to be in an oven).  you can also just through some sieves into your solvent if you grab it out of a sure seal bottle or something that can get it decently dry.  but like I said, if you need extra dry solvents, distillation is the way to go.  hope this helps :)

Offline 408

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Re: How do you dry a solvent...
« Reply #6 on: December 13, 2009, 04:14:16 PM »
As this has not been explicitly mentioned, solvents require different drying agents depending on which is used.  For example it would be a bad idea to use sodium to dry chloroform...

Molecular sieves also can remove water from solvents.

Offline dudeman

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Re: How do you dry a solvent...
« Reply #7 on: December 14, 2009, 05:31:37 PM »
All very good answers... Thanks guys... I tried distillation and it seems to have a great drying effect but I'm sure that some water vapor is passing too since it will evaporate with the solvent. sodium metal sounds need but I was woried about by products that might be left in the solvent then i realized that distillation after using the sodium would solve that problem. Thanks a lot guys. 

Offline bromidewind

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Re: How do you dry a solvent...
« Reply #8 on: December 14, 2009, 07:54:06 PM »
Depending on the solvent, I have had great success using anhydrous sodium sulfate or calcium chloride. Simply adding a small amount to your solvent and stirring until no more clumps form is a good indication that you have a sufficiently dry solvent.

Further distillation (maybe fractional?) is great depending on the boiling temp and complexity of your solvent. Just remember to never never dry an ether all the way in a distillation apparatus!! I have seen shattered apparatuses, with the explosion powerful enough to embed glass shards half way into a tile ceiling.

Offline Al-rasbi

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Re: How do you dry a solvent...
« Reply #9 on: December 16, 2009, 09:22:02 AM »
hi all of you
am working now on my final year project..always i have to dry dichloromethane after extraction.. and i used for that Na2So4 anhydrus..we were using MgSO4 when i was in year4...but my question>>why we dont use the rotary evaporator to dry solvents..?specialy if water was the one with the lower boiling point??[/font]

Offline dudeman

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Re: How do you dry a solvent...
« Reply #10 on: December 17, 2009, 12:39:12 AM »
bromidewind... Thanks for that post. I forgot all about sodium sulfate! That was actually my first post on this forum... I made some and actually used it to dry a one thing that I know of that actually worked. Calcium chloride sparked my interest today but I am a bit weary of the chloride as chlorine is a really reactive chemical. Now I know this isnt pure chlorine but does it react with any chemicals that you know of? For instance... Would it be unwise to dry ammonia gas with calcium chloride?

Al-rasbi... What is special about rotary evaporation?

Offline nj_bartel

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Re: How do you dry a solvent...
« Reply #11 on: December 17, 2009, 02:30:48 AM »
chloride =/= chlorine.

Offline bromidewind

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Re: How do you dry a solvent...
« Reply #12 on: December 17, 2009, 08:06:12 AM »
@ dudeman
Like nj_bartel said above me, chloride is not equal to chlorine. Calcium chloride is an ionic salt, similar to good ol' table salt; although I definitely would not recommend putting calcium chloride on your French fries ;) not because it's toxic but because it's anhydrous. It'd be like eating a chunk of underarm deodorant. Oh, and it also reacts rather exothermically with water, so once it contacts any saliva, you will get some nasty burns. You could probably go ahead and dry that ammonia gas with CaCl2. I've read some literature about using calcium oxide to dry ammonia gas, but they also used ammonium chloride.

@ Al-rasbi
Rotovapping is a great way to dry solvents, but it is rather time consuming. Sodium sulfate is ten times faster, a heck of a lot cheaper, and you don't run the risk of destroying any glassware (unless you have butter fingers). So that's probably why you didn't use the rotovap. My class's lab only had two rotovaps and about twenty students, so you can imagine the long amount of time it took to get all that evaporation done.


Offline nj_bartel

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Re: How do you dry a solvent...
« Reply #13 on: December 17, 2009, 02:02:28 PM »
It should be said that there's often a difference between drying a solvent for lab and drying a solvent for research, particularly when something you're drying is going to be going under inert conditions.  Dissolved oxygen in the solvent isn't even acceptable.

Offline Al-rasbi

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Re: How do you dry a solvent...
« Reply #14 on: December 17, 2009, 03:20:39 PM »
dudeman:
rotary evaporator is an anstrument which is used to rapid evaporating the high boiling point solvents, by the way i like using it.
 

bromideman:
you all right..when i was in year4..i was taking an advanced organic lab course.. we were 30 students and only 4 rotaries..realy we were suffering...but now..because am afinal year student..there is 3 and only 5 or 6 student..


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